Network Working Group N. Popp
Request for Comments: 3367 M. Mealling
Category: Standards Track VeriSign, Inc.
M. Moseley
Netword, Inc.
August 2002
Common Name Resolution Protocol (CNRP)
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract
People often refer to things in the real world by a common name or
phrase, e.g., a trade name, company name, or a book title. These
names are sometimes easier for people to remember and type than URLs.
Furthermore, because of the limited syntax of URLs, companies and
individuals are finding that the ones that might be most reasonable
for their resources are being used elsewhere and so are unavailable.
For the purposes of this document, a "common name" is a word or a
phrase, without imposed syntactic structure, that may be associated
with a resource.
This effort is about the creation of a protocol for client
applications to communicate with common name resolution services, as
exemplified in both the browser enhancement and search site
paradigms. Although the protocol's primary function is resolution,
it is also intended to address issues of internationalization and
localization. Name resolution services are not generic search
services and thus do not need to provide complex Boolean query,
relevance ranking or similar capabilities. The protocol is a simple,
minimal interoperable core. Mechanisms for extension are provided,
so that additional capabilities can be added.
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RFC 3367 Common Name Resolution Protocol (CNRP) August 2002
Several other issues, while of importance to the deployment of common
name resolution services, are outside of the resolution protocol
itself and are not in the initial scope of the proposed effort.
These include discovery and selection of resolution service
providers, administration of resolution services, name registration,
name ownership, and methods for creating, identifying or insuring
unique common names.
For the purposes of this document, a "common name" is a word or a
phrase, without imposed syntactic structure, that may be associated
with a resource. These common names will be used primarily by
humans, as opposed to machine agents. A common name "resolution
service" handles these associations between common names and data
(resources, information about resources, pointers to locations,
etc.). A single common name may be associated with different data
records, and more than one resolution service is expected to exist.
Any common name may be used in any resolution service.
Common names are not URIs (Uniform Resource Identifiers) in that they
lack the syntactic structure imposed by URIs; furthermore, unlike
URNs, there is no requirement of uniqueness or persistence of the
association between a common name and a resource. (Note: common
names may be expressed in a URI, the syntax for which is described in
RFC 3368 [9].)
This document will define a protocol for the parameterized resolution
necessary to make common names useful. "Resolution" is defined as
the retrieval of data associated (a priori) with descriptors that
match the input request. "Parameterized" means the ability to have a
multi-property descriptor. Descriptors are not required to provide
unique identification, therefore 0 or more records may be returned to
meet a specific input query.
2. Important Notes2.1 Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [7].
2.2 DTD is Definitive
The descriptive portions of this document contain pieces of XML that
are *illustrative examples only*. Section 5 of this document
contains the XML DTD for CNRP, which is definitive. If any
discrepancies are found, the DTD wins.
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RFC 3367 Common Name Resolution Protocol (CNRP) August 20022.3 Uniform Resource Identifiers
All URIs used within the CNRP protocol MUST adhere to the
'absoluteURI' production found in the ABNF of [3]. CNRP does not
define the semantics of a Base and therefore is not capable of
expressing the 'URI-Reference' production.
3. Interaction Model3.1 Services, Servers, Datasets and Referrals
CNRP assumes a particular interaction model where a generalized
"service" provides common name resolution at one or more actual
"servers". If the data contained in all its servers is identical
(mirrors), the service need not identify any particular subset of
data. If, however, the service provides different collections of
data through different servers (e.g., subsets, specialized
collections, etc.), it SHOULD indicate what subsets of its data that
each server offers. This is done by using URIs to uniquely
disambiguate one dataset from another. If the service offers a copy
of a collection of data on agreement with a foreign service, the
foreign service SHOULD provide a dataset URI to allow the collection
to be identified as related to its own offerings.
CNRP supports the concept of referrals. This is where a server can
know that another Service exists, within the same Service or
elsewhere, that can provide further answers to a particular query but
decides to forward that fact onto the client instead of chaining the
query for the client. A referral is sent along with the rest of the
results from a server (if any). Referrals to a service SHOULD
indicate the particular dataseturi that triggered the referral, if it
is known. See Section 4.2.5 for details on referrals and loop
detection.
3.2 Requests and Responses
The protocol consists of a simple request/response mechanism. A
client sends one of a few types of requests to a server which
responds with the results of that request. All requests and
responses are encoded with XML [8] using the DTD found in Section 5.
There are two types of requests. One is a general query for a
common-name. The other is a request for an object that describes the
service and its capabilities. There is only one type of response
which is a set of results. Results can contain actual result items,
referrals and/or status messages.
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RFC 3367 Common Name Resolution Protocol (CNRP) August 20023.3 Transport Independence
CNRP is completely encapsulated within its XML definition, and is
therefore transport-independent in its specification. However,
clients need to have a clearly defined means of bootstrapping a
connection with a server.
It is possible to define special-purpose applications that use CNRP
but which never need the HTTP bootstrapping method outlined below;
those applications MUST define how to find the appropriate
server/port/protocol. CNRP servers dedicated to those applications
may provide service only on the ports/transport protocols defined by
the application.
All other (generic) CNRP clients and servers MUST support the HTTP
(Section 7.1) transport on the default CNRP port of 1096.
Note that a particular service may choose to change to a different
transport or port via statements within a CNRP service description
request, but with initial contacts between a client and a server
being over HTTP on port 1096. For a short explanation of how CNRP
employs HTTP, see Section 7.1 of this document. If other transports
are used, they MUST be handled over a port other than the default
CNRP port.
3.4 Character Encoding
To guarantee interoperability, the following provisions apply:
o XML queries and responses MUST be encoded as UTF-8.
Note: As in any XML document, numeric character references may be
used.
o The encoding of characters in the CNRP URI is based on UTF-8; for
details, please see [9].
Any interfaces electing to present/accept protocol elements in other
representations are responsible for accurate transcoding for use in
CNRP protocol elements, per the above provisions.
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RFC 3367 Common Name Resolution Protocol (CNRP) August 20023.5 Queries
Queries are sent by the client to the server. There are two types of
queries.
1. A `special' initial query that establishes the schema for a
particular CNRP database and communicates that to the client.
The CNRP client will send this query, and in turn receive an XML
document defining the query properties that the database
supports. (In CNRP, XML [8] is used to define and express all
objects.) This query is called the 'servicequery' in the DTD.
In the case where a client does not know anything about the
Service, the client MAY assume that it can at least issue the
request via HTTP.
2. A `standard' query, which is the submission of the CNRP search
string to the database. The query will conform to the schema
that MAY have been previously retrieved from the service.
There will be a set of query properties, listed below, treated as
hints by the server. Note: a CNRP database will accept any correctly
encoded CNRP query property; the extent to which a query result is
responsive to those properties is a service differentiator. The base
properties that are always supported are common name, language,
geography, category, and range (start and length of the result set).
CNRP allows database service providers to create unique data types
and expose them to any CNRP client via the CNRP schema XML documents.
3.6 Hints
A hint is an assertion by the user about himself, herself or itself
and the context in which he/she/it is operating. There is no data
type `hint'; a hint is expressed within the structure of the query
itself and is limited or enabled by the richness of the defined query
namespace. In effect, a query and any property within it is a hint.
For example, the "language" property can be given as a hint in a
query; this may be used to order search results. If one wants
results first in US English followed by European French and finally
South American Spanish, the following can be included in the query:
<property name="language" type="rfc1766">en-US</property>
<property name="language" type="rfc1766">fr-FR</property>
<property name="language" type="rfc1766">sp-MX</property>
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RFC 3367 Common Name Resolution Protocol (CNRP) August 2002
Note that the property statements say nothing about whether the
language is primary, secondary, etc. In this example, the ordering
of the statement controls that--the first statement, being first,
means that US English is the primary language. The second statement
specifies the second region/language, and so on. *But this is only
an example.* The extent to which hints are supported (or not) is a
service differentiator.
The fact that a hint exists does not mean that a CNRP database must
respond to it. This best-effort approach is similar to relevance
ranking in a search engine (high precision, low recall); hints are
similar to a search engine's selection criteria. CNRP services will
attempt to return the results "closest" to the selection criteria.
This is quite different from a SQL database approach where a SQL
query returns the entire results set and each result in the set must
match all the requirements expressed by the qualifier (the SQL WHERE
clause).
4. Object Model4.1 Properties
In CNRP, objects are property lists. A property is a named
attribute. A property also has a well-defined type. Some properties
can be part of the query or the results list or both. For
simplicity, CNRP is limiting property values to string values.
4.1.1 Core Properties
CNRP introduces a set of core properties. Core properties are the
minimal set of properties that all CNRP services MUST support in
order to reach CNRP compliance. Hence, the core properties define
the level of interoperability between all CNRP services. The core
properties are:
1. CommonName: the common name associated with a resource.
2. ID: an opaque string that serves as a unique identifier for a
result from a Service (typically a database ID). The ID is not
globally unique, nor necessarily persistent (e.g., between
queries at a given Service).
3. resourceURI: An 'absoluteURI' as defined in the collected ABNF
found in RFC 2396 [3].
4. description: A free text description of the resource.
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RFC 3367 Common Name Resolution Protocol (CNRP) August 20024.1.2 Abstract and Custom Properties
In addition to core properties, CNRP introduces the notion of
abstract properties. The abstract property element provides schema
extensibility beyond the core properties. The notion of abstract
property is extremely important in CNRP since it enables a wider
range of CNRP based services than those based on the core properties.
To create concrete custom properties, a CNRP service must define a
property name and a property type. Therefore, there are really two
ways to create a custom property. The first way is to create a new
property name and define at least one type for it. Another way is to
extend an existing property by defining a new type. The "geography"
property discussed in the next section is an example of a multi-type
property. Note that a type is only applicable to the property it is
defined for. If a new property is defined, a new type MUST be
defined even though the value set for that type may be identical to
an existing type for an existing property. In other words, types are
scoped to a given property. Custom properties MUST be registered
with IANA. Details about the registration process for new properties
can be found in Section 10.
For example, let us assume that a CNRP service specialized on online
books would like to introduce the ISBN property of type "number".
This property would encapsulate the ISBN number of the book online
and would have he following XML representation:
<property name="isbn" type="number">92347231</property>
4.1.3 Base Properties
Illustrating the use of abstract property to extend the core schema,
CNRP also defines a set of custom properties called base properties.
In order to keep the requirements extremely simple, these properties
are not mandatory to implement to reach CNRP compliance. Although,
these properties are not required, it is expected that many services,
especially large ones, will implement them. An equally important
goal for introducing additional properties is to provide a results
filtering mechanism. This is a requirement for large namespaces that
contain several million names.
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RFC 3367 Common Name Resolution Protocol (CNRP) August 2002
The base properties and their types are defined in Appendix A but
listed here for clarity:
o Language:
The language associated with a resource. The default type of this
property is 'RFC1766' and the vocabulary is drawn from the list of
languages in RFC 1766 [4]. If RFC 1766 is updated, then the
values listed in the updated version are also valid for this type.
o Geography:
The geographical region or location associated with a resource.
Some of the possible types are listed below. See Appendix A for a
complete list of types specified by this document.
* 'freeform': a free form expression for a geographical location
(e.g., "palo alto in california").
* 'ISO3166-1': geographical region expressed using a standard
country code as defined by ISO3166-1 (e.g., "US").
* 'ISO3166-2': value = a geographical region expressed using a
standard region and country codes as defined by ISO3166-2
(e.g., "US-CA").
* 'lat-long': the latitude and longitude of a geographical
location.
o Category:
The category associated with a resource. There are large numbers
of possible types for this property. Two possible ones are:
1. 'freeform': a free form expression for a category (e.g.,
"movies").
2. 'NAICS': The North American Industry Code System.
o Range:
The range is a results set control property. The range property
is used to specify the starting point and the length of a results
set (e.g., I want 5 records starting at the 10th record). It
should only ever have one type but, in the interest of
extensibility and consistency, others can be created if there is a
need. The default type is 'start-length' which takes the form of
two integers separated by a dash. The first integer is the
starting number and the second is the number of values to include.
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RFC 3367 Common Name Resolution Protocol (CNRP) August 2002
o Dataseturi: An absoluteURI (as defined in [3] that identifies a
defined set of Common Names and associated data.
Note: For many properties the default "type" is "freeform". The free
form type value is important because it allows very simple user
interface where the user can enter a value in a text field. It is up
to the service to interpret the value correctly and take advantage of
it to increase the relevance of results (using specialized
dictionaries for instance).
4.1.4 Common Name String Encoding and Equivalence Rules
CNRP specifies that common name strings should be encoded using UTF-
8. CNRP does not specify any string equivalence rules for matching a
common name in the query against a common name of a Resource. String
equivalence rules are language and service dependent. They are
specific to relevance ranking algorithms, hence treated as CNRP
services. Consequently, string equivalence rules are not part of the
CNRP protocol specification. For example, the query member:
<commonname>bmw</commonname>
should be read as a selection criterion for a resource with a common
name LIKE (similar to) the string "bmw" where the exact definition of
the LIKE operator is intuitive, yet specific to the queried CNRP
service.
It is also important to note that XML treats whitespace as a special
case in many situations. In some cases, it collapses whitespace into
a single space. Both client and server Implementors are warned to
reference the XML standard for the various ramifications of using
whitespace in queries and/or results.
4.2 Objects4.2.1 Query
The Query object encapsulates all the query components such as
CommonName, ID, and any properties. A Query cannot be empty. A
Query must contain either one and only one common name, or one and
only one ID. A Query can also contain the custom properties defined
by a specific CNRP service.
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RFC 3367 Common Name Resolution Protocol (CNRP) August 2002
For example, a query for the first 5 resources whose common name is
like "bmw" would be expressed as:
<query>
<commonname>bmw</commonname>
<property name="range" type="start-length">1-5</property>
</query>
4.2.1.1 Logical Operations Within a Query
The Query syntax is extremely simple. CNRP does not extensively
support Boolean logic operator such as OR, AND or NOT. However,
there exist two implicit logical operations that can be expressed
through the Query object and its properties. First, a query with
multiple property-value pairs implicitly expresses an AND operation
on the query terms. For instance, the CNRP query to request all the
resources whose common name is like "bmw", AND whose language is
"German" can be expressed as:
<query>
<commonname>bmw</commonname>
<property name="language" type="rfc1766">
de-DE
</property>
</query>
Note however, that because the server is only trying to best match
the Query criteria, there is no guarantee that all or any of the
resources in the results match both requirements.
In addition, CNRP allows the client to express a logical OR by
specifying multiple values for the same property within the Query.
For example, the logical expression:
property = value1 OR property = value2 OR property = valueN
Will be expressed as:
<property>value1</property>
<property>value2</property>
<property>valueN</property>
So if there are different properties expressed, CNRP ANDs them; if
there are multiples instances of the same property expressed, CNRP
ORs them.
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RFC 3367 Common Name Resolution Protocol (CNRP) August 2002
It is important to underline that this form is only applicable to
properties (with the exception of the CommonName itself which, even
though it is a property, is the entire point of the query). In
particular, logical OR operations on the common name are not
supported. Note that the ordering or the property-value pairs in the
query implies a precedence. As a consequence, CNRP also introduces
one special string value: "*". Not surprisingly, "*" means all
admissible values for the typed property. For example, the following
query requests all the resources whose common name is like BMW and
whose language is preferably in German or French or any other
language.
<query>
<commonname>bmw</commonname>
<property name="language" type="rfc1766">de-DE</property>
<property name="language" type="rfc1766">fr-FR</property>
<property name="language" type="rfc1766">*</property>
</query>
4.2.2 Results
The results object is a container for CNRP results. The type of
objects contained in Results can be: ResourceDescriptor, Error,
Referral and Schema. Results from a CNRP service are ordered by
decreasing relevance. When the results set contains results from
multiple CNRP services, the results can no longer be ordered (since
relevance ranking is specific to a given service). In that case,
however, note that results originating from the same service remain
ordered.
4.2.2.1 ResourceDescriptor
The ResourceDescriptor object describes an Internet resource (e.g., a
Web page, a person, any object identified by a URI). Therefore, the
ResourceDescriptor MUST always include the resourceURI property. The
ResourceDescriptor can also contain the commonname, URI, ID (the ID
of this entry in the service's database), description, language,
geography, and category of the resource. A ResourceDescriptor can
also be augmented using custom properties and can reference a service
object to indicate its origin (using the serviceRef element). As
with referrals, a resourcedescriptor block can also contain an ID
attribute that is used by a status message to refer to a particular
resourcedescriptor. Be careful not to confuse this ID with the id
tag itself which refers to the database id of the actual database
entry.
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RFC 3367 Common Name Resolution Protocol (CNRP) August 2002
<results>
<service id="i0">
<serviceuri>http://cnrp.bar.com/</serviceuri>
</service>
<resourcedescriptor id="i1">
<commonname>bmw</commonname>
<id>foo.com:234364</id>
<resourceuri>http://www.bmw.de/</resourceuri>
<serviceref ref="i0" />
<description>BMW Motorcycles, International</description>
<property name="language" type="rfc1766">de-DE</property>
</resourcedescriptor>
<referral>
<serviceref ref="i0" />
</referral>
</results>
4.2.3 Service
The Service object provides an encapsulation of an instance of a CNRP
service. A service is uniquely identified through the serviceuri tag
which MUST be included in the Service object. A Service object MAY
include a a brief textual description of the service. It MAY include
datasets, servers and custom properties.
<service>
<serviceuri>http://cnrp.foo.com</serviceuri>
<description>foo.com is a CNRP service specialized on cocktail
recipes</description>
</service>
The service object MAY also be extended by including existing
properties to further describe the service. For instance, a service
that focuses on French companies could be expressed as:
<service>
<serviceuri>http://cnrp.foo.com</serviceuri>
<property name="category" type="freeform">companies</property>
<property name="geography" type="ISO3166-1">FR</property>
</service>
4.2.3.1 Datasets
The dataset object represents a set of CN-to-URI mappings. For
example, the database of AOL keywords and their URIs constitute a
dataset. The dataset object allows a CNRP implementation to uniquely
identify the database(s) of mappings that it resolves. In that
respect, the notion of dataset allows a separation between resolution
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RFC 3367 Common Name Resolution Protocol (CNRP) August 2002
and data, providing the mechanism for a CNRP service to resolve
common-names on behalf of another CNRP service or even multiple
services. Conversely, the same dataset can be served by two distinct
CNRP services. Since a CNRP service can resolve names within one or
more datasets, the service object can contain one or more dataset
objects (zero if the dataset is not formally declared).
Within the service object, a dataset is uniquely defined using the
dataseturi property. Other properties, such as language and
description, can describe the dataset further. Like the service
object, the dataset object has an ID attribute associated with it
that is unique within a particular XML message. Like the service
object's ID attribute, this ID is used by resourcedescriptors and
referrals to specify which service and/or dataset they came from or
are referring to.
Any service can be said to have a 'default dataset' which is the
dataset that considered to have been used if a server simply responds
to a client's query that didn't contain a dataset. The 'default
dataset' can also be said to be the only dataset that is used by
Services that don't support datasets at all. This concept is useful
for clients that intend on doing rigorous loop detection by way of
keeping a list of visited service/dataset nodes.
This example illustrates how the service object would look as it
defines two datasets:
<service id="i0">
<serviceuri>http://acmecorp.com</serviceuri>
<dataset id="i1">
<property name="dataseturi">
urn:oid:1.2.3.4.666.5.4.3.1
</property>
<property name="language">en-us</property>
<property name="language">en-gb</property>
</dataset>
<dataset id="i2">
<property name="dataseturi">
urn:oid:1.2.3.4.666.10.9.8.7.6
</property>
<property name="language">fr</property>
</dataset>
</service>
The dataseturi property can also be used within the query as a hint
to the service for the dataset within which the commonname should be
resolved:
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RFC 3367 Common Name Resolution Protocol (CNRP) August 2002
<query>
<commonname>toys r us</commonname>
<property name="dataseturi">urn:oid:1.2.3.4.666.5.4.3.1</property>
</query>
It is important to note that resolution rules (i.e., string
equivalence, relevance ranking, etc.) are likely to be dataset
specific. This is true even if the resolution is provided by the
same service.
Another use of the dataseturi property is in a referral. In that
case, the datasetref tag is used to pinpoint a specific dataset
within the service.
<referral>
<serviceref ref="i0" /><datasetref ref="i1" />
</referral>
While the concept of datasets is important for services wishing to
make their data available via other services, it is important to
remember that the declaration and use of datasets is completely
optional. Compliance with the CNRP protocol does not require a
service object to define or reference any dataset object. The only
requirement for compliance is that a client and/or server know the
format of the particular XML tags and deal with them syntactically.
If it chooses to ignore them, then this is well within its rights.
4.2.3.2 Servers
The service object also encapsulates a list of server objects. The
server object is used to describe a CNRP server or set of servers. A
server is identified through its serveruri. The URI used to identify
a server is not a CNRP URI [9], but instead, is a URI of the scheme
used as the CNRP transport mechanism. I.e., for a CNRP server that
will communicate via the HTTP protocol to the host foo.com on port
6543, the serveruri would be http://foo.com:6543. If some other
information is required in order for the correct transport to be
used, then that information can be communicated via other properties.
Note that a Service MUST have at least one Server that responds on
the default CNRP port in order for a client to get the initial
Service object.
A server can serve one or more datasets declared by its service. The
served databases are specified using the dataseturi property. As for
other objects, a server can be further described using descriptive
properties such as geography and description. The following XML
completes the service definition from the previous example by
defining two CNRP servers. One server is located in the US and the
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RFC 3367 Common Name Resolution Protocol (CNRP) August 2002
other is located in France. The US server is specialized and only
serves the French dataset.
<servers>
<server>
<serveruri>cnrp://router.us.widgetco.com:4321</serveruri>
<property name="geography" type="ISO3166-1">US</property>
</server>
<server>
<serveruri>cnrp://router.fr.acmeco.com:4321</serveruri>
<property name="geography" type="ISO3166-1">FR</property>
</server>
</servers>
As we will see in a following section, the Service object can contain
Schema objects. These Schema objects fully describe the query and
response interfaces implemented by a CNRP service. In that regard,
the Service object is essential to discoverability. It constitutes
the main entry point for a CNRP client to dynamically discover the
capabilities of a resolution service. For that purpose, the Service
object can be returned as part of the response to any resolution
query. Furthermore, the Service object is the dedicated response to
the specialized servicequery (see Section 4.2.6).
Another use of Service is for other objects to indicate their CNRP
service of origin. System messages, referrals and
resourcedescriptors can include a reference to their Service object.
For example, imagine a CNRP service that acts as a proxy for multiple
CNRP services. For example, it is a requirement that CNRP allows
aggregation of results from different sources. Consider one such
CNRP service that acts as a proxy for multiple CNRP services. In
this mode, the proxy service contacts each CNRP sub-service in
parallel or serially. Then, the proxy combines the individual result
sets into a unique response returned to the CNRP client. Since the
aggregate result set contains resourcedescriptors from different
services, the proxy adds a servicereference tag within each
individual result to indicate their service of origin. In the event
one of the referred services resolves names within multiple datasets,
it is possible for these objects to refer to a specific dataset
within the service by using the datasetref tag. This example is of a
hybrid result set with resourcedescriptors referencing their service
and dataset of origin:
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RFC 3367 Common Name Resolution Protocol (CNRP) August 2002
</cnrp>
4.2.4 Status Messages4.2.4.1 Status of CNRP, Not the Transport
The status messages defined here are only applicable to operations
defined by CNRP itself. If some feature or operation is defined by
the transport (security via HTTP, mail failure via SMTP, etc.), then
any status messages about that operation MUST be sent in accordance
with that transport's reporting mechanism and not via CNRP.
4.2.4.2 Codes and Description
A Status object indicates a message to the client in the results set.
The object encapsulates two values: a status code and a description.
The description can contain a textual description of the status being
communicated. In many cases, additional diagnostic information can
also be included. No attempt is made to standardize the description
of a given status code since the only programmatic element that
matters is the actual code.
A status message can also specify which other CNRP element it refers
to by including a reference to the ID of the element in question.
For example, if a Service block has an ID of "i2" and a status
message refers to that block, then it can put that ID in its ref
attribute.
<status code="x.y.z" ref="i2">
The CNRP foo.com database is temporarily unreachable
</status>
4.2.4.3 Status Codes
The organization of status codes is taken from RFC 1893 [10] which
structures its codes in the form of x.yyy.zzz. Taken from RFC 1893
is the ABNF for the codes:
status-code = class "." subject "." detail
class = "2"/"3"/"4"/"5"
subject = 1*3digit
detail = 1*3digit
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The top level codes denote levels of severity of the status:
o 1.X.X Informational
* The information conveyed by the code has no bearing or
indication of the success or failure of any request. It is
strictly for informational purposes only.
o 2.X.X Success
* The request was processed and results were returned. In most
cases, this status class won't be sent since actual results
themselves denote success. In other cases, results were
returned but some information needs to be returned to the
client.
o 3.X.X Partial Success
* The request was processed and results were returned. In this
case though, some values sent with the request were either
invalid or ignored but in a way that the server still considers
the response to be a successful one and not indicative of any
true error condition.
o 4.X.X Transient Failure
* The request was valid as sent, but some temporary event
prevents the successful completion of the request and/or
sending of the results. Sending in the future may be possible.
o 5.X.X Permanent Failure
* A permanent failure is one which is not likely to be resolved
by re-sending the request in its current form. Some change to
the request or the destination must be made for successful
request.
The second level codes denote the subject of the status messages.
This value applies to each of the five classifications. The subject
sub-code, if recognized, must be reported even if the additional
detail provided by the detail sub-code is not recognized. The
enumerated values for the subject sub-code are:
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RFC 3367 Common Name Resolution Protocol (CNRP) August 2002
o X.0.X Other or Undefined Status
* No specific information is available about what subject class
this message belongs to.
o X.1.X Query Related
* Any status related to some specific way in which the query was
encoded or its values with the exception of properties.
o X.2.X Service Related
* Any status related to the service in which this server is
cooperating in providing.
Appendix B contains a list of all predefined status codes
4.2.5 Referral
A Referral object in the results set is a place holder for un-fetched
results from a different service and possibly dataset. Referrals
typically occur when a CNRP server knows of another service capable
of providing relevant results for the query and wants to notify the
client about this possibility. The client can decide whether it
wants to follow the referral and resolve the extra results by
contacting the referred-to service using the information contained
within the Referral object (a Service object and possible
properties). The Referral is a simple mechanism to enable
hierarchical resolution as well as to join multiple resolution
services together.
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RFC 3367 Common Name Resolution Protocol (CNRP) August 2002
<results>
<service id="i0">
<serviceuri>http://cnrp.bar.com/</serviceuri>
<dataset id="i1">
<property name="dataseturi">
urn:oid:1.3.6.1.4.1.782.1
</property>
</dataset>
<dataset id="i2">
<property name="dataseturi">
urn:oid:1.3.6.1.4.1.782.2
</property>
</dataset>
</service>
<resourcedescriptor>
<commonname>bmw</commonname>
<id>foo.com:234364</id>
<resourceuri>http://www.bmw.de/</resourceuri>
<serviceref ref="i0" /><datasetref ref="i1" />
<description>BMW Motorcycles, International</description>
<property name="language" type="iso646">de-DE</property>
</resourcedescriptor>
<referral>
<serviceref ref="i0" /><datasetref ref="i2" />
</referral>
</results>
Like other CNRP objects, a referral can be further described using
custom properties. Like a resourcedescriptor, a referral can have an
ID attribute that is used by a status message to talk about a
particular referral block.
4.2.5.1 Loop Detection and Dataset Handling in Servers
Referrals in CNRP can be handled in three ways:
o application specific,
o as hints only,
o rigorous loop detection.
In the first two cases, the behavior of the client, when it receives
a referral, is not defined in this memo. The client can chase the
referral in such a way as to treat it as a hint only. In this case,
datasets may or may not be handled. Loop detection can be nothing
more than, "Have I talked to this hostname before?" or "Stop after
the 3rd referral". These two cases are most likely to apply to
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RFC 3367 Common Name Resolution Protocol (CNRP) August 2002
simple or constrained implementations where the clients and servers
have some a priori knowledge of their capabilities. Without such
knowledge there is too much ambiguity vis-a-vis services and datasets
for clients to do reliable loop detection.
The last case is where the client expects to talk to multiple servers
that may know nothing about each other. This case expresses the
basic semantics of what a server should tell a client if it
understands datasets or referrals. Since a referral specifies the
exact dataset to which it is referring, a node in the list of visited
nodes is made up of a serviceuri and a dataseturi. Both of these
values need to be considered during loop detection. In the case
where a service does not support datasets, the visited node is made
up of the service and the 'default dataset'.
The major thing to remember when doing loop detection across servers
is that some servers may not understand datasets at all, while others
specifically rely on them. To help determine how loop detection
nodes should be marked, three specific status messages have been
defined:
The 3.1.3 (Datasets not supported) status message is used to denote
that the server does not support datasets at all. It is sent in
response to a query containing datasets. The client should consider
that the server ignored the datasets and the client should consider
this node to have been visited for all possible datasets (including
the 'default' dataset).
The 3.1.4 (First dataset only supported) status message is used by a
server to indicate the situation where a client has included several
dataseturis in its query and the server can only support one at a
time. In this case, the server is explicitly stating that it used
the first dataseturi only. The client should consider that only the
first dataseturi specified was processed correctly. The client
should consider that the remaining datasets in the query were ignored
completely. They would need to be sent individually as referrals if
the client really cares about those results. Only the first
serviceuri/dataseturi pair should be marked as visited.
The 3.1.5 (This dataset not supported) status message is used to
indicate that a specific dataseturi sent in a query by a client is
not supported by the server. This serviceuri/dataseturi pair should
be considered as visited by the client. If this message is sent in
reply to a query specifying multiple datasets, the client should
behave the same as if it received the 3.1.3 message from above. It
should be considered bad form for a server to send this status
message back in response to a query with multiple datasets because it
is ambiguous.
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RFC 3367 Common Name Resolution Protocol (CNRP) August 2002
While there is no exact algorithm for loop detection that clients are
encouraged to support, these status messages can be used by the
server to be clear about what Services and Datasets it considers to
have been queried. It is up to the client to decide what to do with
these messages and how closely it attempts to do loop detection.
4.2.6 Discoverability: ServiceQuery and Schema
A subclass of Query, the ServiceQuery object supports the dynamic
discovery of a specific CNRP service's characteristics. Note that
CNRP compliance does not require that a service fully implements
discoverability. In particular, returning the Service object with
its serviceuri constitutes a minimal yet sufficient compliant
implementation. Nevertheless, we expect that advanced CNRP services
will choose to return a full description of their supported
interfaces.
The complete response to a servicequery returns the Service object
described in section 5.3.2 with the following schema information:
1. The base and custom properties used by the CNRP service (Property
schema),
2. The properties used to describe the Service object (Service
schema),
3. The properties that belong to the query interface (Query schema),
4. The properties that belong to a resource within the results
(Resource schema).
These leads to the following new object definitions:
o propertyschema -- A property schema describes all the custom
properties that are part of the service.
o propertydeclaration -- A property declaration describes a base or
custom property used by the CNRP service. A property declaration
has a name and a type (the name and the type of the property that
it refers to). Note that as part of the property schema, one MUST
declare both existing and newly defined properties.
o propertyreference -- A property reference is a reference to a
property declaration so that a given schema (a service, query or
resource schema) can declare the property within its interface.
Note that a property reference specify whether the use of the
property is required or optional only.
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RFC 3367 Common Name Resolution Protocol (CNRP) August 2002
o serviceschema -- The service schema defines the properties used to
describe the service.
o queryschema -- A query schema describes the structure of a query
handled by the CNRP service. The properties referred within the
query schema are part of the query interface of the resolution
service.
o resourcedescriptorschema -- A ResourceDescriptor schema describes
the resource returned as a result by the CNRP service.
For example, a CNRP query to discover a service's capabilities will
be in the form:
<cnrp> <servicequery/> </cnrp>
And for a CNRP service for cocktail recipes in French, the
corresponding response would be:
<service>
<serviceuri>http://cnrp.recipe.com</serviceuri>
<propertyschema>
<propertydeclaration id="i1">
<propertyname>language</propertyname>
<propertytype>rfc1766</propertytype>
</propertydeclaration>
<propertydeclaration id="i2">
<propertyname>cocktailrecipe</propertyname>
<propertytype>freeform</propertytype>
</propertydeclaration>
</propertyschema>
<queryschema>
<propertyreference required="yes" ref="i1"/>
</queryschema>
<resourcedescriptorschema>
<propertyreference required="yes" ref="i1"/>
<propertyreference required="yes" ref="i2"/>
</resourcedescriptorschema>
</service>
This response stipulates that the service accepts the property
language as part of the query interface and returns
resourcedescriptors that contain both the language and cocktailRecipe
properties.
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RFC 3367 Common Name Resolution Protocol (CNRP) August 2002
<serviceuri>http://serverfarm.acmecorp.com</serviceuri>
</service>
<service id="i2">
<serviceuri>http://servers.acmecorp.co.uk</serviceuri>
</service>
<resourcedescriptor>
<commonname>Fidonet</commonname>
<id>1333459455</id>
<resourceuri>http://www.fidonet.ca</resourceuri>
<serviceref ref="i0" />
<description>This is ye olde Canadian Fidonet</description>
</resourcedescriptor>
<resourcedescriptor>
<commonname>Fidonet</commonname>
<id>1333459455</id>
<resourceuri>http://host:port/bla</resourceuri>
<serviceref ref="i1" />
<description>An old Fidonet node</description>
</resourcedescriptor>
<referral><serviceref ref="i2" /></referral>
<status code="3.1.1">
The language property 'fr-CA' was ignored
</status>
</results>
</cnrp>
7. Transport
Two CNRP transport protocols are specified. HTTP is used due to its
popularity and ease of integration with other web applications. SMTP
is also used as a way to illustrate a protocol that has a much
different range of latency than most protocols.
In the cases where transports use MIME Media Types (HTTP and SMTP
being examples of such), the CNRP payload MUST use the
'application/cnrp+xml' media type. See Section 8 for the
registration template for this media type. One important note about
this media type is that, since CNRP always uses UTF-8, there is no
charset attribute.
7.1 HTTP Transport
The HTTP transport is fairly simple. The client connects to an HTTP
based CNRP server and issues a request using the POST method to the
"/" path with the Content-type and Accept header set to
"application/cnrp+xml". The content of the POST body is the CNRP XML
document that is being sent. All HTTP 1.1 features are allowed
during the request.
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RFC 3367 Common Name Resolution Protocol (CNRP) August 2002
The results are sent back to the client with a Content-Type of
"application/cnrp+xml". The body of the result is the CNRP XML
document being sent to the client.
7.2 SMTP Transport
The SMTP transport is very similar to the HTTP transport. Since
there is no method to specify, the CNRP XML document is simply sent
to a particular SMTP endpoint with its Content-Type set to
"application/cnrp+xml". The server responds by sending a response to
the originator of the request with the results in the body and the
Content-Type set to "application/cnrp+xml". The Service MUST specify
at least one SMTP target (email address) to contact.
8. Registration: application/cnrp+xml
This is the registration template for 'application/cnrp+xml' per [6].
MIME media type name: application
MIME subtype name: cnrp+xml
Required parameters: none
Optional parameters: none
Encoding considerations: This media type consists of 8bit text which
may necessitate the use of an appropriate content transfer
encoding on some transports. Since these considerations are the
same as XML in general, RFC3023's [6] discussion of XML and MIME
is applicable.
Security considerations: none specific to this media type. See
Section 9 for general CNRP considerations.
Interoperability considerations: n/a
Published specification: This media type is a proper subset of the
the XML 1.0 specification [8] except for the limitations placed on
tags and encodings by this document.
Applications which use this media type: any CNRP client/server
wishing to send or receive CNRP requests or responses
Additional Information: none
Contact for further information: c.f., the "Author's Address" section
of this memo
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RFC 3367 Common Name Resolution Protocol (CNRP) August 2002
Intended usage: limited use
Author/Change controller: the IESG
9. Security Considerations
Three security threats exist for CNRP or applications that depend on
it: Man in the Middle attacks, malicious agents posing as a service
by spoofing a Service object, and denial of service attacks caused by
adding a new level of indirection for resolution of a resource.
The proposed solution for man in the middle attacks is to utilize
transport level authentication and encryption, where available. In
the case where the transport can't provide the level of required
authentication, individual entries or the entire response can be
signed/encrypted using XML signature methods being developed by the
XMLDSIG Working Group.
In the case of where a service attempts to pose as another by
spoofing the serviceuri in the Service object, the Service object
should be signed. A client can then verify the Service object's
veracity by verifying the signature. How the client obtains that
authoritative public key is out of scope since it depends on the
service discovery problem.
While this document cannot propose a solution for Denial Of Service
(DOS) attacks, it can illustrate that, like many other cases, any
time a new level of indirection is created, an opportunity for a DOS
attack is created. Service providers are encouraged to be aware of
this and to act accordingly to mitigate the effects of a DOS attack.
10. IANA Considerations
The major consideration for the IANA is that the IANA will be
registering well known properties, property types and status
messages. It will not register values. Since this document does not
discuss CNRP service discovery, the IANA will not be registering the
existence of servers or Server objects.
There are three types of entities the IANA can register: properties,
property types, and status messages. If a property or type is not
registered with the IANA, then they must start with "x-". Status
messages can be created for local consumption and not registered.
There is no requirement that new status messages are mandatory to
implement unless this document is updated. Status message
registrations are more for informational purposes.
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RFC 3367 Common Name Resolution Protocol (CNRP) August 2002
The required information for the registration of a new property is
the property's name, its default type, and a general description. A
new type requires the type's name, what properties it is valid for,
and a description. A new status message requires the X.Y.ZZZ code
and a brief description of the state being communicated.
All properties, types and status messages are registered on a First
Come First Served basis with no review by the IANA or any group of
experts. The consensus opinion of the CNRP Working Group is that
review of property registrations should occur once there is
operational experience with the protocol and an actual need for the
review. If, at some future date, this policy needs to change, this
document will be updated.
The property and type registration templates found in Appendix A
should be registered by the IANA at publication time of this
document.
The IANA is also directed to register the Media Type specified in
Section 8.
References
[1] United States, "North American Industry Classification System",
January 1997, <http://www.census.gov/epcd/www/naics.html>.
[2] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L.,
Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol --
HTTP/1.1", RFC 2616, June 1999.
[3] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396, August
1998.
[4] Alvestrand, H., "Tags for the Identification of Languages", RFC1766, March 1995.
[5] Moats, R., "URN Syntax", RFC 2141, May 1997.
[6] Murata, M., St. Laurent, S. and D. Kohn, "XML Media Types", RFC3023, January 2001.
[7] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[8] Bray, T., Paoli, J. and C. Sperberg-McQueen, "Extensible Markup
Language (XML) 1.0", February 1998.
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RFC 3367 Common Name Resolution Protocol (CNRP) August 2002Appendix A. Well Known Property and Type Registration TemplatesA.1 Properties
Property Name: geography
Default Type: iso3166-1
Description: A geographic location
Property Name: language
Default Type: rfc1766
Description: A language specification
Property Name: category
Default Type: freeform
Description: A node in some system of semantic relationships that is
considered relevant to the common-name.
Property Name: range
Default Type: range
Description: A range given in the format "x,y" where x is the
starting point and y is the length. This property is used by the
client to tell the server that is is requesting a subrange of the
results.
Property Name: dataseturi
Default Type: uri
Description: A URI used to disambiguate between two Datasets offered
by the same Service.
A.2 Types
Type: freeform
Property: category
Description: The value is to be interpreted by the server the best
way it knows how. This value has no defined structure.
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Type: freeform
Property: geography
Description: The value is to be interpreted by the server the best
way it knows how. This value has no defined structure.
Type: freeform
Property: language
Description: The value is to be interpreted by the server the best
way it knows how. This value has no defined structure.
Type: iso3166-2
Property: geography
Description: The combination of country and sub-region codes found in
ISO 3166-2 [11].
Type: iso3166-1
Property: Geography
Description: Country Codes found in ISO 3166-1 [11].
Type: postalcode
Property: Geography
Description: A postal code that is valid for some region. A good
example is the Zip code system used in the US.
Type: lat-long
Property: Geography
Description:
Values for latitude and longitude shall be expressed as decimal
fractions of degrees. Whole degrees of latitude shall be
represented by a two-digit decimal number ranging from 0 through
90. Whole degrees of longitude shall be represented by a decimal
number ranging from 0 through 180. When a decimal fraction of a
degree is specified, it shall be separated from the whole number
of degrees by a decimal point. Decimal fractions of a degree may
be expressed to the precision desired.
Latitudes north of the equator shall be specified by a plus sign
(+), or by the absence of a minus sign (-), preceding the
designating degrees. Latitudes south of the Equator shall be
designated by a minus sign (-) preceding the two digits
designating degrees. A point on the Equator shall be assigned to
the Northern Hemisphere.
Longitudes east of the prime meridian shall be specified by a plus
sign (+), or by the Longitudes west of the meridian shall be
designated by minus sign (-) preceding the digits designating
degrees. A point on the prime meridian shall be assigned to the
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RFC 3367 Common Name Resolution Protocol (CNRP) August 2002
Eastern Hemisphere. A point on the 180th meridian shall be
assigned to the Western Hemisphere. One exception to this last
convention is permitted. For the special condition of describing
a band of latitude around the earth, the East Bounding Coordinate
data element shall be assigned the value +180 (180) degrees.
Any spatial address with a latitude of +90 (90) or -90 degrees
will specify the position at the North or South Pole,
respectively. The component for longitude may have any legal
value.
With the exception of the special condition described above, this
form is specified in Department of Commerce, 1986, Representation
of geographic point locations for information interchange (Federal
Information Processing Standard 70-1): Washington, Department of
Commerce, National Institute of Standards and Technology.
DEGREES = *PLUSMINUS DIGITS '.' DIGITS
PLUSMINUS = + | -
DIGITS = DIGIT *DIGIT
DIGIT = 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
Type: rfc1766
Property: Language
Description: language codes as defined by RFC 1766 [4]
Type: naics
Property: Category
Description: North American Industry Code System [1]
Type: uri
Property: dataseturi
Description: A URI adhering to the 'absoluteURI' production of the
Collected ABNF found in [3]
Appendix B. Status CodesB.1 Level 1 (Informative) Codes
1.0.0 -- Undefined Information
This code is used for any non-categorizable and informative
message. If, for example, the server wanted to tell the client
that the systems administrator's cat has blue hair, then this code
would be the appropriate place for this information.
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RFC 3367 Common Name Resolution Protocol (CNRP) August 2002
1.1.0 -- Query related information
This code is used for any informative information concerning the
query that client sent. For example, "The query you sent was
rather interesting!".
1.2.0 -- An informative message pertaining to the Service
This message concerns the Service in the general sense.
B.2 Level 2 (Success) Codes
2.0.0 -- Something undefined succeeded
There was success but the situation that this message concerns is
undefined.
2.1.0 -- Query succeeded
The query succeeded. This message MUST be returned when there
were no results that matched the query. I.e., the query was
successfully handled and the correct set of results contained no
resources or referrals. The lack of results is not an error but a
successful statement about the common-name.
Note: The apparent lack of 2.X.X level codes is caused by success
usually being indicated not by a status message but by the server
returning only the objects that the client requested.
B.3 Level 3 (Partial Success) Codes
3.0.0 -- Something undefined was only partially successful
Some request by the client was only partially successful. The
exact situation or cause of that partial failure is not defined.
3.1.0 -- The query was only partially successful.
3.1.1 -- The query contained invalid or unsupported properties
The query contained invalid or unsupported property names, types
or values. The invalid properties were ignored and the query
processed.
3.1.2 -- The XML was well formed but invalid
The XML sent by the client was well formed but invalid. The
server was smart enough to figure out what the client was talking
about and return some results.
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RFC 3367 Common Name Resolution Protocol (CNRP) August 2002
3.1.3 Server does not support datasets
This status should be generated by servers that do not handle
datasets. A server can send this status message at any time, but
it especially useful for when a server receives a query from a
client that contains a dataseturi. In this case and if the client
is doing rigorous loop detection, the client should consider this
entire service to have been visited.
3.1.4 The first dataset in the list of datasets you gave in the
query was the only one used.
This status message is used by a server to indicate the situation
where a client has included several dataseturis in its query and
the server can only support one at a time. In this case the
server is explicitly stating that it used the first dataseturi
only. The client should consider that only the first dataseturi
specified was processed correctly. The client should consider
that the remaining datasets in the query were ignored completely.
They would need to be sent individually as referrals if the client
really cares about those results. Only the first
serviceuri/dataseturi pair should be marked as visited if loop
detection is being handled.
3.1.5 This dataset not supported.
This message is used to indicate that a specific dataseturi sent
in a query by a client is not supported by the server. This
serviceuri/dataseturi pair should be considered as visited by the
client. If this message is sent in reply to a query specifying
multiple datasets, the client should behave the same as if it
received the 3.1.3 message from above. It should be considered
bad form for a server to send this status message back in response
to a query with multiple datasets because it is ambiguous.
3.2.0 -- The server caused a partially successful event
Due to some internal server error, the results returned were
incomplete.
3.2.1 -- Some referral server was unavailable
This status message is used to denote that one or more of the
referral services that are normally queried was unavailable.
Results were generated, but they may not be representative of a
complete answer.
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RFC 3367 Common Name Resolution Protocol (CNRP) August 2002B.4 Level 4 (Transient Failure) Codes
4.0.0 -- Something undefined caused a persistent transient failure.
4.1.0 -- There was an error in the query that made it unable to be
interpreted.
4.2.0 -- The query was to complex
The query as specified was too complex for this Service to handle.
4.2.1 -- The Service was too busy
Due to resource constraints, the entire service is too busy to
handle requests. This means that any of the Servers cooperating
in providing this Service would have also returned this same
message.
4.2.2 -- The Server is in maintenance
This server is now in maintenance mode. Try another server from
this service or try again at a later time.
4.2.3 -- The Server had an internal error
There was an internal error that caused the server to fail
completely.
B.5 Level 5 (Permanent Failures) Codes.
5.0.0 -- Something undefined caused a permanent failure.
5.1.0 -- The query permanently failed.
5.2.0 -- The service had a permanent failure.
5.2.1 -- This Service is no longer available.
This Service has decided to no longer make itself available.
5.2.2 -- The Server had a permanent failure.
This server has permanently failed. Try another server from this
service.
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RFC 3367 Common Name Resolution Protocol (CNRP) August 2002
Full Copyright Statement
Copyright (C) The Internet Society (2002). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
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Popp, et. al. Standards Track [Page 42]